In H.264/MPEG-4 AVC, one picture is divided into macroblocks to encode an image, the respective macroblocks are encoded by generating a prediction block using inter prediction or intra prediction. The difference between an original block and the prediction block is transformed to generate a transformed block, and the transformed block is quantized using a quantization parameter and one of a plurality of predetermined quantization matrices. The quantized coefficient of the quantized block are scanned by a predetermined scan type and then entropy-coded. The quantization parameter is adjusted per macroblock and encoded using a previous quantization parameter.
Meanwhile, techniques using various size of coding unit are introduced to improve the coding efficiency. Techniques increasing a number of intra prediction modes are also introduces to generate a prediction block more similar to an original block.
But, if the number of intra prediction modes increases, the amount of coding bits required for signaling the intra prediction mode becomes larger. Also, if the size of the coding unit is larger, the difference between an original block and a prediction block prediction block is greater.
Accordingly, more effective method is required to signal the intra prediction mode. More effective method is also required to minimize the difference between the original block and the prediction block and to minimize the coding bits of residual block.